Underfloor heating in SA – the time has come

Despite initial resistance in the uptake of underfloor heating systems locally, the commercial hydronic market in particular is finally taking off for applications far and wide.

There are two main types of underfloor heating systems: wet (hydronic) and dry (electrical). A hydronic system pumps warm water through pipes beneath the floor to create heat, while an electrical system uses electric coils under the floor to achieve its warmth.

The pattern in which hydronic piping is installed is crucial, as unlike electrical underfloor heating, the heat spreads through the pipe gradually. Therefore, the pattern plays a large part in ensuring the room is heated evenly.Image credit: Warmup

I used to consider underfloor heating as part of the plumbing domain; as something that had little relevance to the HVAC&R industry — despite obviously putting the ‘H’ in ‘HVAC&R’. I simply hadn’t seen many of these systems around before.

Now, this is not the first time that I have attempted to do a heating feature. Every time I had this whim, I was met with little enthusiasm from all sides, as people told me that South Africa does not really care as much for heating as many northern hemisphere countries do. Fair enough. Our weather is comparatively far more pleasant, being spared from the north’s excessively brutal winters. That does not mean we do not need underfloor heating, though.

From all accounts, the domestic market has exploded as the emerging middle class demands the comforts of underfloor heating, finally accepting the fact that the initial capital outlay will pay for itself in what it saves in electricity compared to less efficient ways of heating.

Although the South African electrical underfloor heating market has been in existence for quite a long time, it’s in terms of hydronic systems that things have truly picked up over the past five years or so — especially in commercial and industrial applications. From the foyer of the PwC tower to hunching over the floor in the Woolworths store in Kyalami Corner, Midrand, where you can feel the heat with one hand while the other side is planted on a cold spot.

Electrical offers a lower capital investment but hydronic is much cheaper to run.

We chat to various industry role players, ranging from contractors and installers to suppliers and manufacturers, to get some tips on the dos and don’ts of underfloor heating. Here’s what the experts had to say …

The figures

According to a Global Market Insights research report, the global underfloor market was worth USD4 806.53-million in 2016, with massive growth forecasted for the next couple of years. The hydronic underfloor heating market size is set to exceed USD5-billion by 2024.

Their research splits the global market as follows (2016 figures):

Electric: 38.22%

Hydronic: 61.78%

When broken down by region, Africa (grouped together with the Middle East, as always) represents only about 2% of the market. These are the figures:

Europe: 47.30%

North America: 25.14%

Asia Pacific: 23.32%

Middle East and Africa (MEA): 2.14%

Latin America: 2.10%

The official growth summary of the report states: “Growing consumer awareness towards energy conservation, along with significant increase in urban population, will augment the underfloor heating market.

“Declining capital cost along with advancements in technology will further complement the industry landscape. Rising energy consumption, especially across the residential sector, will boost the product demand.”

Why underfloor heating?

It is important to note that underfloor heating systems are radiant, which means they do not heat or move the air. Instead, the radiation directly heats up the objects inside and the environment itself, such as the walls, tables, chairs and, of course, the people.

Underfloor heating also offers the benefit of being hidden out of sight. Unlike other types of heaters, they do not take up wall space or affect where furniture can be placed, as they are hidden beneath the floor itself. Because they spread under the entire area, there are no warm and cold spots close to and far away from the heater.

Heat pumps seem to be the most cost effective for smaller systems, with pellet boilers becoming more feasible the bigger the system becomes (generally above 30kW).

Although underfloor heating has often received a bad rap in South Africa, it is actually the most efficient form of heating, explains Ray Tewson, managing director of Warmup, a local manufacturer and supplier of underfloor heating systems. “Also, not only is it efficient, the comfort levels you get are unmatched when compared to other forms heating,” he says.

Albie Schröder of Pioneer Floor Heating agrees: “Underfloor heating systems are by far a more energy efficient way of heating, as heat rises naturally,” he explains. “As soon as you start going into other forms of convection heating, you require 15–20% more energy to achieve the same comfort levels as generating heat from a floor.”

Schröder has been around the block and is involved not only on the contracting and installation side, but also on the product manufacturing and supplying side. He says they have seen a definite increase in the popularity of particularly hydronic underfloor heating systems. “Hydro has been around 12–15 years locally. But it’s really only over the past five years that the market on hydro floor heating has exploded. Not just commercially, but also domestically,” he explains.

Off to a slow start

With so many obvious benefits, why isn’t underfloor heating more popular in South Africa then?

The biggest resistance to hydro was the fact that the first companies who brought it into the country, didn’t install it correctly and ever since, it has had a bad reputation. “Up until very recently, architects still questioned whether hydronic underfloor heating actually works,” says Schröder. “This was a big issue from the start. People are also worried about leaks and there has been resistance. But now slowly but surely, the architects are getting used to it,” says Schröder.

Wolfgang Stöhr of EcoSmart, a company specialising in integrated heating solutions, agrees. It was hard to get into the market initially, especially with using pellet boilers as the heat source (something they specialise in). “The architects were not willing to recommend the products to their clients. The clients had to be approached directly and convinced that the products were great and cost saving. For us, the biomass boilers and heating combination is becoming more popular and is finally being specified by many architects. It was slow progress in the beginning, though.”

EcoSmart moved into the commercial and industrial market this year as well. As such, Stöhr has been focusing on meeting with engineers across the country to talk to them about the product. “Out of maybe 100 engineers, architects, and quantity surveyors I saw, only two even knew that the biomass boiler integrated with hydronic water underfloor heating option existed!” says Stöhr.

Underfloor heating is definitely gaining popularity now, Stöhr says. “The only reason people are still putting in electrical, is because they don’t know that better options are available.”

Cost is a big issue. One of the biggest challenges the heating market faces, is the fact that the majority of particularly the domestic market cannot actually afford the product, explains Neil Britz of Crown Technologies, HVAC contracting specialists. “And because we only need it for a few months in the year (unlike Europe and colder climates), it is seen as a luxury item, rather than a must-have. But this is slowly changing as the improvements inf underfloor systems are noticeably increasing.”

There is a misconception about heating in the market, explains Tewson. “Although heating is only usually used for three months a year in South Africa, it is calculated as an annual cost, lumping it together with air-conditioning cooling costs as well.” Because of this, all types of radiant electric floor heating are seen as expensive to run and people instead spend money on less energy-efficient heating solutions such as oil heaters, electric bar heaters, gas heaters, and split air-conditioning units, instead of investing in a longer-term, more efficient solution for heating their home.

“Even if a client cannot afford the hydronic solution, it is important to advise them to put in electrical radiant floor heating as it is still more efficient and cost-effective than any of the alternatives,” explains Tewson.

Various configurations of hydronic underfloor heating systems are available. A buffer storage tank with exchanger coil is one of the most common ones. Image credit: Warmup

Hydro vs electrical

“Before the electricity prices went up in South Africa, everyone used to install electrical underfloor heating,” explains Stöhr. “Most people still don’t know that there is an alternative solution available in hydronic underfloor heating.” This means that many people have put in electrical underfloor heating for large areas but never use it because it is too expensive to run.

When it comes to choosing between hydronic and electrical underfloor heating systems, there are pros and cons to both. Simplified, electrical offers a lower capital investment but hydronic is much cheaper to run.

As such, electrical is preferred for smaller areas while hydro is good for bigger spaces and especially applications that require heating 24/7. When it comes to smaller applications like a bathroom, which only needs heating for maybe three months of the year, electrical will work out cheaper.

“Hydronic floor heating doesn’t lend itself to small areas,” Schröder agrees. “It’s not worth the costs.” He says that generally, for anything bigger than 100m2, hydronic starts making sense and the running costs start balancing out the initial investment. But once you drop below 100m2, the costs escalate exponentially.

It is important to note that for retrofit applications, electrical underfloor is probably your best bet as hydronic requires about an extra 40–50mm floor height, which will affect the entire building levels, including things like doors and stairs.

Although currently about 90% of the products that Warmup sells into the local market are still for electrical underfloor heating systems, the hydronic side is growing fast, in particularly the commercial and industrial markets, explains Tewson.

Electric floor heating is sold through many channels, often as a pre-made DIY product such as under-carpet heating pads where the pre-made unit can simply be positioned on top of the underlay under the carpet. “Heating specialists seldom get involved with this type of installation,” says Tewson. “However, hydronic and electric under tile and under floor heating is much more specialised and requires a heating expert to handle the installation.”

Pioneer Floor Heating manufactures and installs both hydronic and electrical underfloor heating systems across the country. Schröder explains that they started off with electrical, as hydronic wasn’t really available locally and the price of electricity was still negligible. But these days, about 70% of their business is hydronic systems.

Although Pioneer still moves about 450kW of electrical product every month in Johannesburg and surrounds, he explains that this is more for domestic and smaller, spot heating applications.

“The hydronic system is by far the best system available, both for comfort and for running costs,” Stöhr says. “The savings enjoyed from the running costs over an extended period, normally at least 50 years (when using the best systems), far exceeds the savings on installation costs.”

Installation cost may be further reduced for hydronic heating when installing an integrated biomass boiler system for all domestic hot water needs, as well as pool, Jacuzzi, radiator, towel rail, or fan coil heating.

Applications

Other than the usual domestic application, the possibilities for underfloor radiant heating are vast, explains Schröder.

Pioneer has been involved in many commercial applications, including the PwC tower in Midrand, the extension of the Rosebank Mall, Freedom Park, some government buildings, and even piping containers to be shipped for living quarters. Currently, they are busy with the Brits Hospital’s staff accommodation, which boasts in excess of 86km of piping just for the hydronic system.

They have also been involved with providing underfloor heating for Woolworths. But here the heat is generated by means of heat recovery, virtually free as there is no heat source. The heat is generated as a by-product of the CO2 trans-critical refrigeration plant. The hot CO2 generated from the refrigerated plant is directed through a heat exchanger, which generates the hot water that is pumped back into the floor system. Thus, the only running cost comes from the circulation pump.

The Crown Technologies team have quoted on anything from yoga studios to butterfly farms and everything in-between. As the heat rises from the floor, it works particularly well in applications with large open areas and double-volume spaces, like airports for example, Britz says.

Electrical heating in particular works well in chicken batteries, explains Tewson. They have been supplying a number of hatcheries for many years now, improving the mortality rate of day-old chicks significantly. Traditionally, a large heat source is installed and the chicks huddle around it when it gets cold and as much as half of them die from dehydration within the first week. So, they installed underfloor heating instead and not only did it prevent the chicks from dying, their slaughter date moved up by a week as they could feed day and night now. It worked so well that underfloor heating was installed in seven more of that farmer’s hatcheries.

Crocodile farms, veterinary clinic animal recovery enclosures, saunas, and so much more. If you require heating, underfloor is a good choice. Even frost protection of the surface below cold-storage rooms — there is a need for underfloor heating to prevent the sub-floor from freezing, cracking, and lifting, as well as preventing ice from building up, causing items either to stick to the floor or slide on slippery hazardous surfaces.

Choosing the right system

Before designing an underfloor heating system, it is important to know what you are working with. Firstly, you need to know the heat load of the area and how much heating is required, explains Britz.

Within any building, there would be a demand for a certain wattage per square metre, depending on the building’s insulation and other contributing factors such as the type of bricks used and the resistance it offers. This helps the team calculate the size of the system. But as it can be tricky to get exact information from a client, they generally work on providing 100W per square metre.

You also need to look at running costs — how many hours a year the system will be required to run. This makes a huge difference because, as mentioned, electrical underfloor heating costs less to install while the running costs of hydronic is lower.

It is important to determine how many loops and pipes would be required for the system. According to Britz, the ideal pipe run is around 100m — 120m at a push. Anything bigger and you risk heat losses and pressure drops, making the system inefficient. Also, the more loops you have, the bigger the manifold has to be and the more actuators and hardware you need. For bigger areas, they would rather install multiple zones to get the most efficient solution.

Choosing your heat source

There is more to underfloor heating than just the piping, though. How efficient and how effective your system is, will all depend on the heat source behind it.

Crown Technologies prefers heat pumps as a heat source as opposed to solar, specifically where you would need a large footprint. Not only that: with solar, it is hard to design for both summer and winter conditions without wasting any heat. That is why they often suggest hybrid systems, combining solar and heat pumps. By means of diversion of heat generated by solar collectors, it is possible to warm Jacuzzis or swimming pools, using the heat pumps as backup for periods of overcast weather.

“Heat pumps are still the most efficient heat source; you get the best coefficient of performance (COP) for the type of installations we do,” explains Britz.

Pioneer also prefers using heat pumps as a heat source. “It offers the best capital layout versus running cost,” says Schröder. He recently did a running cost comparison for a client, comparing the various heat sources and found heat pumps were by far the best value for money in the long term when compared to pellet boilers, electricity, and LPG gas.

Solar is still tricky to use as a heat source on its own, as there is no way to store the energy and you need the energy at night when the sun doesn’t shine, explains Schröder. “The main duty cycle of an underfloor heating system is at night when the solar system is non-collective.”

Schröder calculated that for a 200m2 underfloor system, you have to store 128kW of power to run that system during the night. “It’s not impossible, but it will be expensive. Prolonged bad weather will affect the system too and you will need a backup anyway. So, you might as well just put in a heat pump.”

When designing an underfloor system, it is important to get the most out of your heat source. Heat pumps do not like stop-starting and would rather run for longer periods, less frequently. As such, Pioneer designs these systems with a buffer tank rather, because generally, every time you have a circuit calling for hot water, the heat pump engages for one or two minutes and then switches off, stressing the compressor. You would rather have it come on once or twice an hour and run for 10 minutes and get the buffer tank up to temperature again and then switch off again. “It reduces the number of start-ups on the machine by 50–60%, which has a direct impact on the life expectancy of the machine,” says Schröder.

EcoSmart also used to link their systems to heat pumps as the heat source but now prefer using pellet boilers as they consider these more efficient. “The problem with heat pumps is that they still use energy, even when not on.”

When a client had a concern that the system was still using a lot of energy, Stöhr put a meter on the heat pump to track its energy usage. They found that the heat pump used 0.483kW just because it was on — not even when it was heating the water. It used almost 12kWh a day just by being on, which is not usually taken into account when calculating the efficiency of a heat pump. “The COPs are done under perfect conditions; it doesn’t take all other factors into account,” explains Stöhr.

Boiler pellets are made from waste wood from processing. EcoSmart buys pellets from Pietermaritzburg and ships them to Cape Town to supply their clients. Last year, they supplied 1 000 tonnes of pellets. “It costs the client 60c per 1kWh produced energy wise if they use pellets,” said Stöhr. “That is much cheaper, at least half, than if they were using a heat pump.”

The more things you heat with the pellet boiler, the quicker your return on investment. According to Stöhr, around 30kW is the dividing point — at 30kW the pellet boiler and heat pump capital outlay are pretty much on par. “Anything bigger than that and the pellet boiler starts becoming cheaper.” It is a good investment for large installations like apartment blocks, or housing developments. They are currently doing an apartment block where they can reduce the electrical connection by 50% because they went for pellet burners instead of heat pumps in the end.

“What a heat pump uses in three days in winter, our pellet systems would use in a year, electricity wise,” says Stöhr. With 1kg of pellets, you can generate 5.4kWh of energy. A tonne, which takes up roughly 1.2m3 of space, gives you 5 400kWh.

Note: Every single supplier I spoke to, provided their own calculations to prove in rand for watt value which system is more efficient. Some preferred heat pumps, some pellet boilers. Heat pumps seem to be the most cost effective for smaller systems, with pellet boilers becoming more feasible the bigger the system becomes. In the end, it will depend on the application. So, do your research for what you would need!

Not all pipes are equal

In terms of piping, you get what you pay for, says Schröder. But it is worth investing in imported piping with a 50-year guarantee. “The piping is built in under the slab; you want it to last at least 50 years.” Pioneer mainly uses cross-polymer PEX pipe out of Europe. It is a multilayer cross-link pipe with three layers: two cross-linked layers of PEX and an oxygen EVOH barrier.

These systems are all closed-loop systems and they get filled once. A water treatment takes place, which displaces the oxygen out of the water so you don’t have bacterial growth in the piping structure. If you do not use an oxygen-barrier pipe, you will have limited amounts of oxygen seepage through the actual wall of the pipe over prolonged periods. After a year or two, this will render your water treatment system useless, explains Schröder.

One of the most important things to consider when designing an underfloor heating system, is the temperature of the water that goes to the floor, explains Stöhr. The higher the temperatures used, the faster the deterioration of the water underfloor heating pipes. High water temperatures will heat the floor and thereby the room much faster; however, it will also be more difficult to control the set temperature of the room.

The pipes deteriorate due to the changes in temperature when heating and allowing the pipes to cool down, before heating again. “If you do it right, your pipes will last a minimum of 50 years, maybe even 100 years.”

You have to calculate the water temperature according to the requirement and application, but it is generally 37–42°C —you shouldn’t be going higher than that, Stöhr advises. Though, there are exceptions.

Dos and don’ts — tips

The various experts interviewed have learnt a lot over the many years spent manufacturing, supplying, designing, and installing underfloor heating systems in this country. This is their advice for getting the most efficient, most effective systems.

Step one, as mentioned, is ensuring your pipe runs are not too long. Schröder advises that depending on the amount of bends, he is willing to go up to a 110m pipe run in one circuit. “Anything longer and the pressure drop becomes too high and the change in temperature too drastic. We aim to have a fixed-degree delta T temperature drop of 10°C over the circuit.”

Step two is making sure it is designed for the right capacity, Britz explains. If the system is designed under capacity in terms of the heat source, the area will never quite heat up enough and it will shorten the life expectancy of the equipment. Or if the wrong circuit breaker is installed, it will not be able to handle the heat source and it will keep tripping.

Another issue is not including the underfloor heating as part of the initial design. As it will affect the rest of the building, this has to be considered in the building plans from day one.

It is important to leave the installation of hydronic underfloor heating systems to the professionals, says Schröder. One of the biggest problems is incorrect circuit layouts. He says that often people will just phone up their local plumber to do the job — often to disastrous effect. The plumber will generally just loop a system and then loop the cold water return around, causing an uneven spread of temperature. Instead, you should loop the hot water and do a cold central return in-between the loops. That means an average spread of temperature between high and low. No matter where you are on the floor circuit, there will be an average spread of temperature.

Michael Carter of The Tech Butler, who does radiant heating and cooling installations locally, suggests rendering an energy model of the underfloor heating system before starting your design. This should be done after the heat load calculations.

Before starting on the design, you should also decide whether you are going to have a local thermostat in each room or a centrally controlled system, explains Carter. Other questions to ask before starting include: is there a plant room (or space for a plant room) for the hot water stores? Does the client want a combined hot water and underfloor system or separate systems? Do you require sound absorption?

With the systems that Carter installs, there is the option to either install the pipes in the slab or in the screed. “Pipes installed in the slab are very difficult to repair and there could be heat losses from the edges of the slab,” he explains. “You require less energy to heat a 45mm screed. The screed needs to float and will expand when heated. It requires expansion strips between the walls and the screed.”

“You would need to add 100mm extra to your floor level to accommodate for a hydronic underfloor system,” he advises. A minimum of 45mm for the screed and 55mm for the piping and polystyrene.

Insulation is also key, and you need to be sure whether there is insulation in the slab. For a new build, this is now a non-negotiable requirement; however, it may present a challenge on refurb projects.

He also advises that when installing the piping for an underfloor hydronic system, the pipes should be tested under pressure and left while under construction to ensure that the installer is alerted when any of the pipes are cut accidentally.

The positioning of the manifold distribution boxes is crucial, and Carter advises to make sure they are installed for easy access.

According to Carter, a good rule of thumb to remember is that there is a 4°C difference between your feet and what it feels like at your head. “That’s why 16°C at your feet will feel like 20°C at your head.” That is also why thermostats should be installed head-height.

“Insulation is preventing the cold from coming in and heat from being lost through the floor — which can save you as much as 50% in terms of energy usage.”

Another mistake is when the system is designed with the wrong pump. “We only use energy-efficient variable speed pumps, as they last longer,” says Stöhr. “These adjust to the demand, saving on energy and on wear and tear.”

It is important to choose the right thermostat for your system as they range from basic to quite intelligent. There are simple thermostats, normally not very accurate, and will generally overshoot set temperatures, and then undershoot. The temperature variance in the room could be as much as 4–5°C. This influences energy usage. “The more accurate you get the thermostat, the more energy you will save,” explains Stöhr.

Where possible, the manifold should be centralised to avoid long supply and return lead pipes.

The future / advancements

When it comes to the actual underfloor system, you still get out what you put in, and there isn’t much advancement other than materials becoming thinner and more durable. How efficient your system is will still depend on your heat source.

The main thing that has changed recently is the building regulations and the fact that it is now compulsory for new builds to have insulation, as mentioned. This has increased the efficiency of all types of underfloor heating systems drastically, explains Tewson. Most of your heat loss is through the floor, second through windows, and then through the ceiling. “Insulation is preventing the cold from coming in and heat from being lost through the floor — which can save you as much as 50% in terms of energy usage.”

The major developments and energy saving have come in on the controllers and thermostat side. Thermostats have become ‘smarter’, says Tewson. The advanced, intelligent thermostats are set to your lifestyle and self-adjust accordingly so as to operate as efficiently and effectively as possible. Even telling you how much it is costing you in rand to run a particular system over a particular period. A new range of Wi-Fi and touch-screen thermostats can be controlled remotely from anywhere in the home or around the world.

As with all things, energy efficiency is where most developments are going. But with heating systems, what you put in, is what you get out. That is why Schröder is hopeful of alternative energy solutions in future to provide a better heat source. “Alternative energy sources are where the real innovation lies,” he says. “Piping is piping. Heat sources are the critical thing. Cheap energy is the future.”